The most serious property of cancer is its ability to invade surrounding tissue and spread to new organ systems. Blood-borne metastasis is a highly complex and multifaceted process by which successful tumor cell emboli finally arrest at and invade through the microvessel wall and associated connective tissue matrix. Destruction of the basement membrane of the microvascular endothelium appears to require the production of degradative enzymes by the invading tumor cells. We are examining some of these events, using an in vitro model consisting of human microvascular endothelial cells and human tumor cells. We will isolate and culture microvessel endothelial cells from human dermis according to established techniques. Pure populations of such microvascular endothelial cells can be readily cultured as confluent monolayers and have been shown to retain many of their differentiated characteristics, even after serial passage. Preliminary results suggest that these cells produce a basement membrane-like matrix containing certain specific basement membrane constituents such as laminin, type IV collagen and heparan sulfate proteoglycan. We plan to fully characterize the subendothelial matrix by ultrastructural, biochemical and immunological techniques. The capability of tumor cells to adhere to the endothelial cell surface and isolated matrix will be examined in an attempt to understand the molecular basis of tumor cell implantation and extravasation. The ability of tumor cells to solubilize and degrade the macromolecules (glycoproteins, collagens and proteoglycans) of the subendothelial matrix by the elaboration of proteases and glycosidases will be assayed and directly compared with their similar activities on extracellular matrices and basement membranes produced by other cell types, including fibroblasts, smooth muscle cells and epithelial cells. Tissue explants of human primary and metastatic tumors also will be assayed for their degradative and invasive behavior toward the human microvascular endothelium and subendothelial matrix. These assays may have potential value as diagnostic tools in predicting the invasive and metastatic properties of newly detected neoplasms.